rustc_codegen_ssa/mir/
rvalue.rs

1use itertools::Itertools as _;
2use rustc_abi::{self as abi, BackendRepr, FIRST_VARIANT};
3use rustc_middle::ty::adjustment::PointerCoercion;
4use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
5use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
6use rustc_middle::{bug, mir, span_bug};
7use rustc_session::config::OptLevel;
8use tracing::{debug, instrument};
9
10use super::FunctionCx;
11use super::operand::{OperandRef, OperandRefBuilder, OperandValue};
12use super::place::{PlaceRef, PlaceValue, codegen_tag_value};
13use crate::common::{IntPredicate, TypeKind};
14use crate::traits::*;
15use crate::{MemFlags, base};
16
17impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
18    #[instrument(level = "trace", skip(self, bx))]
19    pub(crate) fn codegen_rvalue(
20        &mut self,
21        bx: &mut Bx,
22        dest: PlaceRef<'tcx, Bx::Value>,
23        rvalue: &mir::Rvalue<'tcx>,
24    ) {
25        match *rvalue {
26            mir::Rvalue::Use(ref operand) => {
27                let cg_operand = self.codegen_operand(bx, operand);
28                // Crucially, we do *not* use `OperandValue::Ref` for types with
29                // `BackendRepr::Scalar | BackendRepr::ScalarPair`. This ensures we match the MIR
30                // semantics regarding when assignment operators allow overlap of LHS and RHS.
31                if matches!(
32                    cg_operand.layout.backend_repr,
33                    BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..),
34                ) {
35                    debug_assert!(!matches!(cg_operand.val, OperandValue::Ref(..)));
36                }
37                // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
38                // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
39                cg_operand.val.store(bx, dest);
40            }
41
42            mir::Rvalue::Cast(
43                mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _),
44                ref source,
45                _,
46            ) => {
47                // The destination necessarily contains a wide pointer, so if
48                // it's a scalar pair, it's a wide pointer or newtype thereof.
49                if bx.cx().is_backend_scalar_pair(dest.layout) {
50                    // Into-coerce of a thin pointer to a wide pointer -- just
51                    // use the operand path.
52                    let temp = self.codegen_rvalue_operand(bx, rvalue);
53                    temp.val.store(bx, dest);
54                    return;
55                }
56
57                // Unsize of a nontrivial struct. I would prefer for
58                // this to be eliminated by MIR building, but
59                // `CoerceUnsized` can be passed by a where-clause,
60                // so the (generic) MIR may not be able to expand it.
61                let operand = self.codegen_operand(bx, source);
62                match operand.val {
63                    OperandValue::Pair(..) | OperandValue::Immediate(_) => {
64                        // Unsize from an immediate structure. We don't
65                        // really need a temporary alloca here, but
66                        // avoiding it would require us to have
67                        // `coerce_unsized_into` use `extractvalue` to
68                        // index into the struct, and this case isn't
69                        // important enough for it.
70                        debug!("codegen_rvalue: creating ugly alloca");
71                        let scratch = PlaceRef::alloca(bx, operand.layout);
72                        scratch.storage_live(bx);
73                        operand.val.store(bx, scratch);
74                        base::coerce_unsized_into(bx, scratch, dest);
75                        scratch.storage_dead(bx);
76                    }
77                    OperandValue::Ref(val) => {
78                        if val.llextra.is_some() {
79                            bug!("unsized coercion on an unsized rvalue");
80                        }
81                        base::coerce_unsized_into(bx, val.with_type(operand.layout), dest);
82                    }
83                    OperandValue::ZeroSized => {
84                        bug!("unsized coercion on a ZST rvalue");
85                    }
86                }
87            }
88
89            mir::Rvalue::Cast(mir::CastKind::Transmute, ref operand, _ty) => {
90                let src = self.codegen_operand(bx, operand);
91                self.codegen_transmute(bx, src, dest);
92            }
93
94            mir::Rvalue::Repeat(ref elem, count) => {
95                // Do not generate the loop for zero-sized elements or empty arrays.
96                if dest.layout.is_zst() {
97                    return;
98                }
99
100                // When the element is a const with all bytes uninit, emit a single memset that
101                // writes undef to the entire destination.
102                if let mir::Operand::Constant(const_op) = elem {
103                    let val = self.eval_mir_constant(const_op);
104                    if val.all_bytes_uninit(self.cx.tcx()) {
105                        let size = bx.const_usize(dest.layout.size.bytes());
106                        bx.memset(
107                            dest.val.llval,
108                            bx.const_undef(bx.type_i8()),
109                            size,
110                            dest.val.align,
111                            MemFlags::empty(),
112                        );
113                        return;
114                    }
115                }
116
117                let cg_elem = self.codegen_operand(bx, elem);
118
119                let try_init_all_same = |bx: &mut Bx, v| {
120                    let start = dest.val.llval;
121                    let size = bx.const_usize(dest.layout.size.bytes());
122
123                    // Use llvm.memset.p0i8.* to initialize all same byte arrays
124                    if let Some(int) = bx.cx().const_to_opt_u128(v, false)
125                        && let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()]
126                        && let Ok(&byte) = bytes.iter().all_equal_value()
127                    {
128                        let fill = bx.cx().const_u8(byte);
129                        bx.memset(start, fill, size, dest.val.align, MemFlags::empty());
130                        return true;
131                    }
132
133                    // Use llvm.memset.p0i8.* to initialize byte arrays
134                    let v = bx.from_immediate(v);
135                    if bx.cx().val_ty(v) == bx.cx().type_i8() {
136                        bx.memset(start, v, size, dest.val.align, MemFlags::empty());
137                        return true;
138                    }
139                    false
140                };
141
142                if let OperandValue::Immediate(v) = cg_elem.val
143                    && try_init_all_same(bx, v)
144                {
145                    return;
146                }
147
148                let count = self
149                    .monomorphize(count)
150                    .try_to_target_usize(bx.tcx())
151                    .expect("expected monomorphic const in codegen");
152
153                bx.write_operand_repeatedly(cg_elem, count, dest);
154            }
155
156            // This implementation does field projection, so never use it for `RawPtr`,
157            // which will always be fine with the `codegen_rvalue_operand` path below.
158            mir::Rvalue::Aggregate(ref kind, ref operands)
159                if !matches!(**kind, mir::AggregateKind::RawPtr(..)) =>
160            {
161                let (variant_index, variant_dest, active_field_index) = match **kind {
162                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
163                        let variant_dest = dest.project_downcast(bx, variant_index);
164                        (variant_index, variant_dest, active_field_index)
165                    }
166                    _ => (FIRST_VARIANT, dest, None),
167                };
168                if active_field_index.is_some() {
169                    assert_eq!(operands.len(), 1);
170                }
171                for (i, operand) in operands.iter_enumerated() {
172                    let op = self.codegen_operand(bx, operand);
173                    // Do not generate stores and GEPis for zero-sized fields.
174                    if !op.layout.is_zst() {
175                        let field_index = active_field_index.unwrap_or(i);
176                        let field = if let mir::AggregateKind::Array(_) = **kind {
177                            let llindex = bx.cx().const_usize(field_index.as_u32().into());
178                            variant_dest.project_index(bx, llindex)
179                        } else {
180                            variant_dest.project_field(bx, field_index.as_usize())
181                        };
182                        op.val.store(bx, field);
183                    }
184                }
185                dest.codegen_set_discr(bx, variant_index);
186            }
187
188            _ => {
189                let temp = self.codegen_rvalue_operand(bx, rvalue);
190                temp.val.store(bx, dest);
191            }
192        }
193    }
194
195    /// Transmutes the `src` value to the destination type by writing it to `dst`.
196    ///
197    /// See also [`Self::codegen_transmute_operand`] for cases that can be done
198    /// without needing a pre-allocated place for the destination.
199    fn codegen_transmute(
200        &mut self,
201        bx: &mut Bx,
202        src: OperandRef<'tcx, Bx::Value>,
203        dst: PlaceRef<'tcx, Bx::Value>,
204    ) {
205        // The MIR validator enforces no unsized transmutes.
206        assert!(src.layout.is_sized());
207        assert!(dst.layout.is_sized());
208
209        if src.layout.size != dst.layout.size
210            || src.layout.is_uninhabited()
211            || dst.layout.is_uninhabited()
212        {
213            // These cases are all UB to actually hit, so don't emit code for them.
214            // (The size mismatches are reachable via `transmute_unchecked`.)
215            bx.unreachable_nonterminator();
216        } else {
217            // Since in this path we have a place anyway, we can store or copy to it,
218            // making sure we use the destination place's alignment even if the
219            // source would normally have a higher one.
220            src.val.store(bx, dst.val.with_type(src.layout));
221        }
222    }
223
224    /// Transmutes an `OperandValue` to another `OperandValue`.
225    ///
226    /// This is supported for all cases where the `cast` type is SSA,
227    /// but for non-ZSTs with [`abi::BackendRepr::Memory`] it ICEs.
228    pub(crate) fn codegen_transmute_operand(
229        &mut self,
230        bx: &mut Bx,
231        operand: OperandRef<'tcx, Bx::Value>,
232        cast: TyAndLayout<'tcx>,
233    ) -> OperandValue<Bx::Value> {
234        if let abi::BackendRepr::Memory { .. } = cast.backend_repr
235            && !cast.is_zst()
236        {
237            span_bug!(self.mir.span, "Use `codegen_transmute` to transmute to {cast:?}");
238        }
239
240        // `Layout` is interned, so we can do a cheap check for things that are
241        // exactly the same and thus don't need any handling.
242        if abi::Layout::eq(&operand.layout.layout, &cast.layout) {
243            return operand.val;
244        }
245
246        // Check for transmutes that are always UB.
247        if operand.layout.size != cast.size
248            || operand.layout.is_uninhabited()
249            || cast.is_uninhabited()
250        {
251            bx.unreachable_nonterminator();
252
253            // We still need to return a value of the appropriate type, but
254            // it's already UB so do the easiest thing available.
255            return OperandValue::poison(bx, cast);
256        }
257
258        // To or from pointers takes different methods, so we use this to restrict
259        // the SimdVector case to types which can be `bitcast` between each other.
260        #[inline]
261        fn vector_can_bitcast(x: abi::Scalar) -> bool {
262            matches!(
263                x,
264                abi::Scalar::Initialized {
265                    value: abi::Primitive::Int(..) | abi::Primitive::Float(..),
266                    ..
267                }
268            )
269        }
270
271        let cx = bx.cx();
272        match (operand.val, operand.layout.backend_repr, cast.backend_repr) {
273            _ if cast.is_zst() => OperandValue::ZeroSized,
274            (OperandValue::Ref(source_place_val), abi::BackendRepr::Memory { .. }, _) => {
275                assert_eq!(source_place_val.llextra, None);
276                // The existing alignment is part of `source_place_val`,
277                // so that alignment will be used, not `cast`'s.
278                bx.load_operand(source_place_val.with_type(cast)).val
279            }
280            (
281                OperandValue::Immediate(imm),
282                abi::BackendRepr::Scalar(from_scalar),
283                abi::BackendRepr::Scalar(to_scalar),
284            ) if from_scalar.size(cx) == to_scalar.size(cx) => {
285                OperandValue::Immediate(transmute_scalar(bx, imm, from_scalar, to_scalar))
286            }
287            (
288                OperandValue::Immediate(imm),
289                abi::BackendRepr::SimdVector { element: from_scalar, .. },
290                abi::BackendRepr::SimdVector { element: to_scalar, .. },
291            ) if vector_can_bitcast(from_scalar) && vector_can_bitcast(to_scalar) => {
292                let to_backend_ty = bx.cx().immediate_backend_type(cast);
293                OperandValue::Immediate(bx.bitcast(imm, to_backend_ty))
294            }
295            (
296                OperandValue::Pair(imm_a, imm_b),
297                abi::BackendRepr::ScalarPair(in_a, in_b),
298                abi::BackendRepr::ScalarPair(out_a, out_b),
299            ) if in_a.size(cx) == out_a.size(cx) && in_b.size(cx) == out_b.size(cx) => {
300                OperandValue::Pair(
301                    transmute_scalar(bx, imm_a, in_a, out_a),
302                    transmute_scalar(bx, imm_b, in_b, out_b),
303                )
304            }
305            _ => {
306                // For any other potentially-tricky cases, make a temporary instead.
307                // If anything else wants the target local to be in memory this won't
308                // be hit, as `codegen_transmute` will get called directly. Thus this
309                // is only for places where everything else wants the operand form,
310                // and thus it's not worth making those places get it from memory.
311                //
312                // Notably, Scalar ⇌ ScalarPair cases go here to avoid padding
313                // and endianness issues, as do SimdVector ones to avoid worrying
314                // about things like f32x8 ⇌ ptrx4 that would need multiple steps.
315                let align = Ord::max(operand.layout.align.abi, cast.align.abi);
316                let size = Ord::max(operand.layout.size, cast.size);
317                let temp = PlaceValue::alloca(bx, size, align);
318                bx.lifetime_start(temp.llval, size);
319                operand.val.store(bx, temp.with_type(operand.layout));
320                let val = bx.load_operand(temp.with_type(cast)).val;
321                bx.lifetime_end(temp.llval, size);
322                val
323            }
324        }
325    }
326
327    /// Cast one of the immediates from an [`OperandValue::Immediate`]
328    /// or an [`OperandValue::Pair`] to an immediate of the target type.
329    ///
330    /// Returns `None` if the cast is not possible.
331    fn cast_immediate(
332        &self,
333        bx: &mut Bx,
334        mut imm: Bx::Value,
335        from_scalar: abi::Scalar,
336        from_backend_ty: Bx::Type,
337        to_scalar: abi::Scalar,
338        to_backend_ty: Bx::Type,
339    ) -> Option<Bx::Value> {
340        use abi::Primitive::*;
341
342        // When scalars are passed by value, there's no metadata recording their
343        // valid ranges. For example, `char`s are passed as just `i32`, with no
344        // way for LLVM to know that they're 0x10FFFF at most. Thus we assume
345        // the range of the input value too, not just the output range.
346        assume_scalar_range(bx, imm, from_scalar, from_backend_ty, None);
347
348        imm = match (from_scalar.primitive(), to_scalar.primitive()) {
349            (Int(_, is_signed), Int(..)) => bx.intcast(imm, to_backend_ty, is_signed),
350            (Float(_), Float(_)) => {
351                let srcsz = bx.cx().float_width(from_backend_ty);
352                let dstsz = bx.cx().float_width(to_backend_ty);
353                if dstsz > srcsz {
354                    bx.fpext(imm, to_backend_ty)
355                } else if srcsz > dstsz {
356                    bx.fptrunc(imm, to_backend_ty)
357                } else {
358                    imm
359                }
360            }
361            (Int(_, is_signed), Float(_)) => {
362                if is_signed {
363                    bx.sitofp(imm, to_backend_ty)
364                } else {
365                    bx.uitofp(imm, to_backend_ty)
366                }
367            }
368            (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
369            (Int(_, is_signed), Pointer(..)) => {
370                let usize_imm = bx.intcast(imm, bx.cx().type_isize(), is_signed);
371                bx.inttoptr(usize_imm, to_backend_ty)
372            }
373            (Float(_), Int(_, is_signed)) => bx.cast_float_to_int(is_signed, imm, to_backend_ty),
374            _ => return None,
375        };
376        Some(imm)
377    }
378
379    pub(crate) fn codegen_rvalue_operand(
380        &mut self,
381        bx: &mut Bx,
382        rvalue: &mir::Rvalue<'tcx>,
383    ) -> OperandRef<'tcx, Bx::Value> {
384        match *rvalue {
385            mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
386                let operand = self.codegen_operand(bx, source);
387                debug!("cast operand is {:?}", operand);
388                let cast = bx.cx().layout_of(self.monomorphize(mir_cast_ty));
389
390                let val = match *kind {
391                    mir::CastKind::PointerExposeProvenance => {
392                        assert!(bx.cx().is_backend_immediate(cast));
393                        let llptr = operand.immediate();
394                        let llcast_ty = bx.cx().immediate_backend_type(cast);
395                        let lladdr = bx.ptrtoint(llptr, llcast_ty);
396                        OperandValue::Immediate(lladdr)
397                    }
398                    mir::CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
399                        match *operand.layout.ty.kind() {
400                            ty::FnDef(def_id, args) => {
401                                let instance = ty::Instance::resolve_for_fn_ptr(
402                                    bx.tcx(),
403                                    bx.typing_env(),
404                                    def_id,
405                                    args,
406                                )
407                                .unwrap();
408                                OperandValue::Immediate(bx.get_fn_addr(instance))
409                            }
410                            _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
411                        }
412                    }
413                    mir::CastKind::PointerCoercion(PointerCoercion::ClosureFnPointer(_), _) => {
414                        match *operand.layout.ty.kind() {
415                            ty::Closure(def_id, args) => {
416                                let instance = Instance::resolve_closure(
417                                    bx.cx().tcx(),
418                                    def_id,
419                                    args,
420                                    ty::ClosureKind::FnOnce,
421                                );
422                                OperandValue::Immediate(bx.cx().get_fn_addr(instance))
423                            }
424                            _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),
425                        }
426                    }
427                    mir::CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer, _) => {
428                        // This is a no-op at the LLVM level.
429                        operand.val
430                    }
431                    mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
432                        assert!(bx.cx().is_backend_scalar_pair(cast));
433                        let (lldata, llextra) = operand.val.pointer_parts();
434                        let (lldata, llextra) =
435                            base::unsize_ptr(bx, lldata, operand.layout.ty, cast.ty, llextra);
436                        OperandValue::Pair(lldata, llextra)
437                    }
438                    mir::CastKind::PointerCoercion(
439                        PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer, _
440                    ) => {
441                        bug!("{kind:?} is for borrowck, and should never appear in codegen");
442                    }
443                    mir::CastKind::PtrToPtr
444                        if bx.cx().is_backend_scalar_pair(operand.layout) =>
445                    {
446                        if let OperandValue::Pair(data_ptr, meta) = operand.val {
447                            if bx.cx().is_backend_scalar_pair(cast) {
448                                OperandValue::Pair(data_ptr, meta)
449                            } else {
450                                // Cast of wide-ptr to thin-ptr is an extraction of data-ptr.
451                                OperandValue::Immediate(data_ptr)
452                            }
453                        } else {
454                            bug!("unexpected non-pair operand");
455                        }
456                    }
457                    | mir::CastKind::IntToInt
458                    | mir::CastKind::FloatToInt
459                    | mir::CastKind::FloatToFloat
460                    | mir::CastKind::IntToFloat
461                    | mir::CastKind::PtrToPtr
462                    | mir::CastKind::FnPtrToPtr
463                    // Since int2ptr can have arbitrary integer types as input (so we have to do
464                    // sign extension and all that), it is currently best handled in the same code
465                    // path as the other integer-to-X casts.
466                    | mir::CastKind::PointerWithExposedProvenance => {
467                        let imm = operand.immediate();
468                        let abi::BackendRepr::Scalar(from_scalar) = operand.layout.backend_repr else {
469                            bug!("Found non-scalar for operand {operand:?}");
470                        };
471                        let from_backend_ty = bx.cx().immediate_backend_type(operand.layout);
472
473                        assert!(bx.cx().is_backend_immediate(cast));
474                        let to_backend_ty = bx.cx().immediate_backend_type(cast);
475                        if operand.layout.is_uninhabited() {
476                            let val = OperandValue::Immediate(bx.cx().const_poison(to_backend_ty));
477                            return OperandRef { val, layout: cast };
478                        }
479                        let abi::BackendRepr::Scalar(to_scalar) = cast.layout.backend_repr else {
480                            bug!("Found non-scalar for cast {cast:?}");
481                        };
482
483                        self.cast_immediate(bx, imm, from_scalar, from_backend_ty, to_scalar, to_backend_ty)
484                            .map(OperandValue::Immediate)
485                            .unwrap_or_else(|| {
486                                bug!("Unsupported cast of {operand:?} to {cast:?}");
487                            })
488                    }
489                    mir::CastKind::Transmute => {
490                        self.codegen_transmute_operand(bx, operand, cast)
491                    }
492                };
493                OperandRef { val, layout: cast }
494            }
495
496            mir::Rvalue::Ref(_, bk, place) => {
497                let mk_ref = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
498                    Ty::new_ref(tcx, tcx.lifetimes.re_erased, ty, bk.to_mutbl_lossy())
499                };
500                self.codegen_place_to_pointer(bx, place, mk_ref)
501            }
502
503            mir::Rvalue::CopyForDeref(place) => {
504                self.codegen_operand(bx, &mir::Operand::Copy(place))
505            }
506            mir::Rvalue::RawPtr(kind, place) => {
507                let mk_ptr = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
508                    Ty::new_ptr(tcx, ty, kind.to_mutbl_lossy())
509                };
510                self.codegen_place_to_pointer(bx, place, mk_ptr)
511            }
512
513            mir::Rvalue::BinaryOp(op_with_overflow, box (ref lhs, ref rhs))
514                if let Some(op) = op_with_overflow.overflowing_to_wrapping() =>
515            {
516                let lhs = self.codegen_operand(bx, lhs);
517                let rhs = self.codegen_operand(bx, rhs);
518                let result = self.codegen_scalar_checked_binop(
519                    bx,
520                    op,
521                    lhs.immediate(),
522                    rhs.immediate(),
523                    lhs.layout.ty,
524                );
525                let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
526                let operand_ty = Ty::new_tup(bx.tcx(), &[val_ty, bx.tcx().types.bool]);
527                OperandRef { val: result, layout: bx.cx().layout_of(operand_ty) }
528            }
529            mir::Rvalue::BinaryOp(op, box (ref lhs, ref rhs)) => {
530                let lhs = self.codegen_operand(bx, lhs);
531                let rhs = self.codegen_operand(bx, rhs);
532                let llresult = match (lhs.val, rhs.val) {
533                    (
534                        OperandValue::Pair(lhs_addr, lhs_extra),
535                        OperandValue::Pair(rhs_addr, rhs_extra),
536                    ) => self.codegen_wide_ptr_binop(
537                        bx,
538                        op,
539                        lhs_addr,
540                        lhs_extra,
541                        rhs_addr,
542                        rhs_extra,
543                        lhs.layout.ty,
544                    ),
545
546                    (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => self
547                        .codegen_scalar_binop(
548                            bx,
549                            op,
550                            lhs_val,
551                            rhs_val,
552                            lhs.layout.ty,
553                            rhs.layout.ty,
554                        ),
555
556                    _ => bug!(),
557                };
558                OperandRef {
559                    val: OperandValue::Immediate(llresult),
560                    layout: bx.cx().layout_of(op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
561                }
562            }
563
564            mir::Rvalue::UnaryOp(op, ref operand) => {
565                let operand = self.codegen_operand(bx, operand);
566                let is_float = operand.layout.ty.is_floating_point();
567                let (val, layout) = match op {
568                    mir::UnOp::Not => {
569                        let llval = bx.not(operand.immediate());
570                        (OperandValue::Immediate(llval), operand.layout)
571                    }
572                    mir::UnOp::Neg => {
573                        let llval = if is_float {
574                            bx.fneg(operand.immediate())
575                        } else {
576                            bx.neg(operand.immediate())
577                        };
578                        (OperandValue::Immediate(llval), operand.layout)
579                    }
580                    mir::UnOp::PtrMetadata => {
581                        assert!(operand.layout.ty.is_raw_ptr() || operand.layout.ty.is_ref(),);
582                        let (_, meta) = operand.val.pointer_parts();
583                        assert_eq!(operand.layout.fields.count() > 1, meta.is_some());
584                        if let Some(meta) = meta {
585                            (OperandValue::Immediate(meta), operand.layout.field(self.cx, 1))
586                        } else {
587                            (OperandValue::ZeroSized, bx.cx().layout_of(bx.tcx().types.unit))
588                        }
589                    }
590                };
591                assert!(
592                    val.is_expected_variant_for_type(self.cx, layout),
593                    "Made wrong variant {val:?} for type {layout:?}",
594                );
595                OperandRef { val, layout }
596            }
597
598            mir::Rvalue::Discriminant(ref place) => {
599                let discr_ty = rvalue.ty(self.mir, bx.tcx());
600                let discr_ty = self.monomorphize(discr_ty);
601                let operand = self.codegen_consume(bx, place.as_ref());
602                let discr = operand.codegen_get_discr(self, bx, discr_ty);
603                OperandRef {
604                    val: OperandValue::Immediate(discr),
605                    layout: self.cx.layout_of(discr_ty),
606                }
607            }
608
609            mir::Rvalue::NullaryOp(ref null_op, ty) => {
610                let ty = self.monomorphize(ty);
611                let layout = bx.cx().layout_of(ty);
612                let val = match null_op {
613                    mir::NullOp::SizeOf => {
614                        assert!(bx.cx().type_is_sized(ty));
615                        let val = layout.size.bytes();
616                        bx.cx().const_usize(val)
617                    }
618                    mir::NullOp::AlignOf => {
619                        assert!(bx.cx().type_is_sized(ty));
620                        let val = layout.align.abi.bytes();
621                        bx.cx().const_usize(val)
622                    }
623                    mir::NullOp::OffsetOf(fields) => {
624                        let val = bx
625                            .tcx()
626                            .offset_of_subfield(bx.typing_env(), layout, fields.iter())
627                            .bytes();
628                        bx.cx().const_usize(val)
629                    }
630                    mir::NullOp::UbChecks => {
631                        let val = bx.tcx().sess.ub_checks();
632                        bx.cx().const_bool(val)
633                    }
634                    mir::NullOp::ContractChecks => {
635                        let val = bx.tcx().sess.contract_checks();
636                        bx.cx().const_bool(val)
637                    }
638                };
639                let tcx = self.cx.tcx();
640                OperandRef {
641                    val: OperandValue::Immediate(val),
642                    layout: self.cx.layout_of(null_op.ty(tcx)),
643                }
644            }
645
646            mir::Rvalue::ThreadLocalRef(def_id) => {
647                assert!(bx.cx().tcx().is_static(def_id));
648                let layout = bx.layout_of(bx.cx().tcx().static_ptr_ty(def_id, bx.typing_env()));
649                let static_ = if !def_id.is_local() && bx.cx().tcx().needs_thread_local_shim(def_id)
650                {
651                    let instance = ty::Instance {
652                        def: ty::InstanceKind::ThreadLocalShim(def_id),
653                        args: ty::GenericArgs::empty(),
654                    };
655                    let fn_ptr = bx.get_fn_addr(instance);
656                    let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
657                    let fn_ty = bx.fn_decl_backend_type(fn_abi);
658                    let fn_attrs = if bx.tcx().def_kind(instance.def_id()).has_codegen_attrs() {
659                        Some(bx.tcx().codegen_instance_attrs(instance.def))
660                    } else {
661                        None
662                    };
663                    bx.call(
664                        fn_ty,
665                        fn_attrs.as_deref(),
666                        Some(fn_abi),
667                        fn_ptr,
668                        &[],
669                        None,
670                        Some(instance),
671                    )
672                } else {
673                    bx.get_static(def_id)
674                };
675                OperandRef { val: OperandValue::Immediate(static_), layout }
676            }
677            mir::Rvalue::Use(ref operand) => self.codegen_operand(bx, operand),
678            mir::Rvalue::Repeat(ref elem, len_const) => {
679                // All arrays have `BackendRepr::Memory`, so only the ZST cases
680                // end up here. Anything else forces the destination local to be
681                // `Memory`, and thus ends up handled in `codegen_rvalue` instead.
682                let operand = self.codegen_operand(bx, elem);
683                let array_ty = Ty::new_array_with_const_len(bx.tcx(), operand.layout.ty, len_const);
684                let array_ty = self.monomorphize(array_ty);
685                let array_layout = bx.layout_of(array_ty);
686                assert!(array_layout.is_zst());
687                OperandRef { val: OperandValue::ZeroSized, layout: array_layout }
688            }
689            mir::Rvalue::Aggregate(ref kind, ref fields) => {
690                let (variant_index, active_field_index) = match **kind {
691                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
692                        (variant_index, active_field_index)
693                    }
694                    _ => (FIRST_VARIANT, None),
695                };
696
697                let ty = rvalue.ty(self.mir, self.cx.tcx());
698                let ty = self.monomorphize(ty);
699                let layout = self.cx.layout_of(ty);
700
701                let mut builder = OperandRefBuilder::new(layout);
702                for (field_idx, field) in fields.iter_enumerated() {
703                    let op = self.codegen_operand(bx, field);
704                    let fi = active_field_index.unwrap_or(field_idx);
705                    builder.insert_field(bx, variant_index, fi, op);
706                }
707
708                let tag_result = codegen_tag_value(self.cx, variant_index, layout);
709                match tag_result {
710                    Err(super::place::UninhabitedVariantError) => {
711                        // Like codegen_set_discr we use a sound abort, but could
712                        // potentially `unreachable` or just return the poison for
713                        // more optimizability, if that turns out to be helpful.
714                        bx.abort();
715                        let val = OperandValue::poison(bx, layout);
716                        OperandRef { val, layout }
717                    }
718                    Ok(maybe_tag_value) => {
719                        if let Some((tag_field, tag_imm)) = maybe_tag_value {
720                            builder.insert_imm(tag_field, tag_imm);
721                        }
722                        builder.build(bx.cx())
723                    }
724                }
725            }
726            mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
727                let operand = self.codegen_operand(bx, operand);
728                let val = operand.immediate();
729
730                let content_ty = self.monomorphize(content_ty);
731                let box_layout = bx.cx().layout_of(Ty::new_box(bx.tcx(), content_ty));
732
733                OperandRef { val: OperandValue::Immediate(val), layout: box_layout }
734            }
735            mir::Rvalue::WrapUnsafeBinder(ref operand, binder_ty) => {
736                let operand = self.codegen_operand(bx, operand);
737                let binder_ty = self.monomorphize(binder_ty);
738                let layout = bx.cx().layout_of(binder_ty);
739                OperandRef { val: operand.val, layout }
740            }
741        }
742    }
743
744    /// Codegen an `Rvalue::RawPtr` or `Rvalue::Ref`
745    fn codegen_place_to_pointer(
746        &mut self,
747        bx: &mut Bx,
748        place: mir::Place<'tcx>,
749        mk_ptr_ty: impl FnOnce(TyCtxt<'tcx>, Ty<'tcx>) -> Ty<'tcx>,
750    ) -> OperandRef<'tcx, Bx::Value> {
751        let cg_place = self.codegen_place(bx, place.as_ref());
752        let val = cg_place.val.address();
753
754        let ty = cg_place.layout.ty;
755        assert!(
756            if bx.cx().tcx().type_has_metadata(ty, bx.cx().typing_env()) {
757                matches!(val, OperandValue::Pair(..))
758            } else {
759                matches!(val, OperandValue::Immediate(..))
760            },
761            "Address of place was unexpectedly {val:?} for pointee type {ty:?}",
762        );
763
764        OperandRef { val, layout: self.cx.layout_of(mk_ptr_ty(self.cx.tcx(), ty)) }
765    }
766
767    fn codegen_scalar_binop(
768        &mut self,
769        bx: &mut Bx,
770        op: mir::BinOp,
771        lhs: Bx::Value,
772        rhs: Bx::Value,
773        lhs_ty: Ty<'tcx>,
774        rhs_ty: Ty<'tcx>,
775    ) -> Bx::Value {
776        let is_float = lhs_ty.is_floating_point();
777        let is_signed = lhs_ty.is_signed();
778        match op {
779            mir::BinOp::Add => {
780                if is_float {
781                    bx.fadd(lhs, rhs)
782                } else {
783                    bx.add(lhs, rhs)
784                }
785            }
786            mir::BinOp::AddUnchecked => {
787                if is_signed {
788                    bx.unchecked_sadd(lhs, rhs)
789                } else {
790                    bx.unchecked_uadd(lhs, rhs)
791                }
792            }
793            mir::BinOp::Sub => {
794                if is_float {
795                    bx.fsub(lhs, rhs)
796                } else {
797                    bx.sub(lhs, rhs)
798                }
799            }
800            mir::BinOp::SubUnchecked => {
801                if is_signed {
802                    bx.unchecked_ssub(lhs, rhs)
803                } else {
804                    bx.unchecked_usub(lhs, rhs)
805                }
806            }
807            mir::BinOp::Mul => {
808                if is_float {
809                    bx.fmul(lhs, rhs)
810                } else {
811                    bx.mul(lhs, rhs)
812                }
813            }
814            mir::BinOp::MulUnchecked => {
815                if is_signed {
816                    bx.unchecked_smul(lhs, rhs)
817                } else {
818                    bx.unchecked_umul(lhs, rhs)
819                }
820            }
821            mir::BinOp::Div => {
822                if is_float {
823                    bx.fdiv(lhs, rhs)
824                } else if is_signed {
825                    bx.sdiv(lhs, rhs)
826                } else {
827                    bx.udiv(lhs, rhs)
828                }
829            }
830            mir::BinOp::Rem => {
831                if is_float {
832                    bx.frem(lhs, rhs)
833                } else if is_signed {
834                    bx.srem(lhs, rhs)
835                } else {
836                    bx.urem(lhs, rhs)
837                }
838            }
839            mir::BinOp::BitOr => bx.or(lhs, rhs),
840            mir::BinOp::BitAnd => bx.and(lhs, rhs),
841            mir::BinOp::BitXor => bx.xor(lhs, rhs),
842            mir::BinOp::Offset => {
843                let pointee_type = lhs_ty
844                    .builtin_deref(true)
845                    .unwrap_or_else(|| bug!("deref of non-pointer {:?}", lhs_ty));
846                let pointee_layout = bx.cx().layout_of(pointee_type);
847                if pointee_layout.is_zst() {
848                    // `Offset` works in terms of the size of pointee,
849                    // so offsetting a pointer to ZST is a noop.
850                    lhs
851                } else {
852                    let llty = bx.cx().backend_type(pointee_layout);
853                    if !rhs_ty.is_signed() {
854                        bx.inbounds_nuw_gep(llty, lhs, &[rhs])
855                    } else {
856                        bx.inbounds_gep(llty, lhs, &[rhs])
857                    }
858                }
859            }
860            mir::BinOp::Shl | mir::BinOp::ShlUnchecked => {
861                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShlUnchecked);
862                bx.shl(lhs, rhs)
863            }
864            mir::BinOp::Shr | mir::BinOp::ShrUnchecked => {
865                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShrUnchecked);
866                if is_signed { bx.ashr(lhs, rhs) } else { bx.lshr(lhs, rhs) }
867            }
868            mir::BinOp::Ne
869            | mir::BinOp::Lt
870            | mir::BinOp::Gt
871            | mir::BinOp::Eq
872            | mir::BinOp::Le
873            | mir::BinOp::Ge => {
874                if is_float {
875                    bx.fcmp(base::bin_op_to_fcmp_predicate(op), lhs, rhs)
876                } else {
877                    bx.icmp(base::bin_op_to_icmp_predicate(op, is_signed), lhs, rhs)
878                }
879            }
880            mir::BinOp::Cmp => {
881                assert!(!is_float);
882                bx.three_way_compare(lhs_ty, lhs, rhs)
883            }
884            mir::BinOp::AddWithOverflow
885            | mir::BinOp::SubWithOverflow
886            | mir::BinOp::MulWithOverflow => {
887                bug!("{op:?} needs to return a pair, so call codegen_scalar_checked_binop instead")
888            }
889        }
890    }
891
892    fn codegen_wide_ptr_binop(
893        &mut self,
894        bx: &mut Bx,
895        op: mir::BinOp,
896        lhs_addr: Bx::Value,
897        lhs_extra: Bx::Value,
898        rhs_addr: Bx::Value,
899        rhs_extra: Bx::Value,
900        _input_ty: Ty<'tcx>,
901    ) -> Bx::Value {
902        match op {
903            mir::BinOp::Eq => {
904                let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
905                let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
906                bx.and(lhs, rhs)
907            }
908            mir::BinOp::Ne => {
909                let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
910                let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
911                bx.or(lhs, rhs)
912            }
913            mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
914                // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
915                let (op, strict_op) = match op {
916                    mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
917                    mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
918                    mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
919                    mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
920                    _ => bug!(),
921                };
922                let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
923                let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
924                let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
925                let rhs = bx.and(and_lhs, and_rhs);
926                bx.or(lhs, rhs)
927            }
928            _ => {
929                bug!("unexpected wide ptr binop");
930            }
931        }
932    }
933
934    fn codegen_scalar_checked_binop(
935        &mut self,
936        bx: &mut Bx,
937        op: mir::BinOp,
938        lhs: Bx::Value,
939        rhs: Bx::Value,
940        input_ty: Ty<'tcx>,
941    ) -> OperandValue<Bx::Value> {
942        let (val, of) = match op {
943            // These are checked using intrinsics
944            mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
945                let oop = match op {
946                    mir::BinOp::Add => OverflowOp::Add,
947                    mir::BinOp::Sub => OverflowOp::Sub,
948                    mir::BinOp::Mul => OverflowOp::Mul,
949                    _ => unreachable!(),
950                };
951                bx.checked_binop(oop, input_ty, lhs, rhs)
952            }
953            _ => bug!("Operator `{:?}` is not a checkable operator", op),
954        };
955
956        OperandValue::Pair(val, of)
957    }
958}
959
960/// Transmutes a single scalar value `imm` from `from_scalar` to `to_scalar`.
961///
962/// This is expected to be in *immediate* form, as seen in [`OperandValue::Immediate`]
963/// or [`OperandValue::Pair`] (so `i1` for bools, not `i8`, for example).
964///
965/// ICEs if the passed-in `imm` is not a value of the expected type for
966/// `from_scalar`, such as if it's a vector or a pair.
967pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
968    bx: &mut Bx,
969    mut imm: Bx::Value,
970    from_scalar: abi::Scalar,
971    to_scalar: abi::Scalar,
972) -> Bx::Value {
973    assert_eq!(from_scalar.size(bx.cx()), to_scalar.size(bx.cx()));
974    let imm_ty = bx.cx().val_ty(imm);
975    assert_ne!(
976        bx.cx().type_kind(imm_ty),
977        TypeKind::Vector,
978        "Vector type {imm_ty:?} not allowed in transmute_scalar {from_scalar:?} -> {to_scalar:?}"
979    );
980
981    // While optimizations will remove no-op transmutes, they might still be
982    // there in debug or things that aren't no-op in MIR because they change
983    // the Rust type but not the underlying layout/niche.
984    if from_scalar == to_scalar {
985        return imm;
986    }
987
988    use abi::Primitive::*;
989    imm = bx.from_immediate(imm);
990
991    let from_backend_ty = bx.cx().type_from_scalar(from_scalar);
992    debug_assert_eq!(bx.cx().val_ty(imm), from_backend_ty);
993    let to_backend_ty = bx.cx().type_from_scalar(to_scalar);
994
995    // If we have a scalar, we must already know its range. Either
996    //
997    // 1) It's a parameter with `range` parameter metadata,
998    // 2) It's something we `load`ed with `!range` metadata, or
999    // 3) After a transmute we `assume`d the range (see below).
1000    //
1001    // That said, last time we tried removing this, it didn't actually help
1002    // the rustc-perf results, so might as well keep doing it
1003    // <https://github.com/rust-lang/rust/pull/135610#issuecomment-2599275182>
1004    assume_scalar_range(bx, imm, from_scalar, from_backend_ty, Some(&to_scalar));
1005
1006    imm = match (from_scalar.primitive(), to_scalar.primitive()) {
1007        (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
1008        (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
1009        (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
1010        (Pointer(..), Int(..)) => {
1011            // FIXME: this exposes the provenance, which shouldn't be necessary.
1012            bx.ptrtoint(imm, to_backend_ty)
1013        }
1014        (Float(_), Pointer(..)) => {
1015            let int_imm = bx.bitcast(imm, bx.cx().type_isize());
1016            bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
1017        }
1018        (Pointer(..), Float(_)) => {
1019            // FIXME: this exposes the provenance, which shouldn't be necessary.
1020            let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
1021            bx.bitcast(int_imm, to_backend_ty)
1022        }
1023    };
1024
1025    debug_assert_eq!(bx.cx().val_ty(imm), to_backend_ty);
1026
1027    // This `assume` remains important for cases like (a conceptual)
1028    //    transmute::<u32, NonZeroU32>(x) == 0
1029    // since it's never passed to something with parameter metadata (especially
1030    // after MIR inlining) so the only way to tell the backend about the
1031    // constraint that the `transmute` introduced is to `assume` it.
1032    assume_scalar_range(bx, imm, to_scalar, to_backend_ty, Some(&from_scalar));
1033
1034    imm = bx.to_immediate_scalar(imm, to_scalar);
1035    imm
1036}
1037
1038/// Emits an `assume` call that `imm`'s value is within the known range of `scalar`.
1039///
1040/// If `known` is `Some`, only emits the assume if it's more specific than
1041/// whatever is already known from the range of *that* scalar.
1042fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
1043    bx: &mut Bx,
1044    imm: Bx::Value,
1045    scalar: abi::Scalar,
1046    backend_ty: Bx::Type,
1047    known: Option<&abi::Scalar>,
1048) {
1049    if matches!(bx.cx().sess().opts.optimize, OptLevel::No) {
1050        return;
1051    }
1052
1053    match (scalar, known) {
1054        (abi::Scalar::Union { .. }, _) => return,
1055        (_, None) => {
1056            if scalar.is_always_valid(bx.cx()) {
1057                return;
1058            }
1059        }
1060        (abi::Scalar::Initialized { valid_range, .. }, Some(known)) => {
1061            let known_range = known.valid_range(bx.cx());
1062            if valid_range.contains_range(known_range, scalar.size(bx.cx())) {
1063                return;
1064            }
1065        }
1066    }
1067
1068    match scalar.primitive() {
1069        abi::Primitive::Int(..) => {
1070            let range = scalar.valid_range(bx.cx());
1071            bx.assume_integer_range(imm, backend_ty, range);
1072        }
1073        abi::Primitive::Pointer(abi::AddressSpace::ZERO)
1074            if !scalar.valid_range(bx.cx()).contains(0) =>
1075        {
1076            bx.assume_nonnull(imm);
1077        }
1078        abi::Primitive::Pointer(..) | abi::Primitive::Float(..) => {}
1079    }
1080}
rustc_codegen_ssa/mir/rvalue.rs

rustc_codegen_ssa/mir/
rvalue.rs
